5o8 



In this, the phenomena of crippling, due to chronic action of cold, no 

 longer come under consideration ; for these phenomena are primarily normal 

 functions which are only retarded gradually by a lack of heat until life 

 becomes extinct\ The matter is quite dififerent in the acute cases where 

 death follows immediately upon the cold. 



In the acute frost phenomena, the formation of ice becomes a consider- 

 able factor. This does not occur, however, at the point where pure water 

 freezes but only below o degrees C, because the cell sap represents a salt 

 solution. Besides this, observations, of which those of Miiller-Thurgau'- 

 especially should be cited, show that ice is produced only after the freezing 

 point has been exceeded to a certain degree, either to an excessive chilling or 

 supercooling. As an example of how often the supercooling point lies 

 considerably below the freezing point, a few statements of the above named 

 investigators may serve as examples. 



In grapes, the freezing point (G) was found to be at 3.1 degrees C. 

 below zero, the supercooling point (U) at 6.7 to /.S degrees C. below zero; 

 in apples and pears, 1.4 to 1.9 degrees C. below zero (G) and 2.1 to 5.1 

 degrees C. below zero (U) ; in potatoes i.o to 1.6 degrees C. below zero (G) 

 and 2.8 to 5.6 degrees C. below zero (U), etc. 



The formation of ice occurs suddenly; therefore, in cases where some 

 supercooling has taken place, there follows a sudden change in temperature. 

 Our hardy plants, which can still grow unimpaired after they have become 

 brittle with ice, show that the formation of ice is fatal only for certain 

 varieties. In other cases, however, it has been observed that parts of plants, 

 under certain conditions, can be cooled down to a still lower temperature 

 and remain alive, while, with lesser cold, but dififerent conditions, they are 

 frozen as soon as the formation of ice has taken place. 



This formation of ice, the process of which we have already described 

 thoroughly, is now ascribed by Miiller-Thurgau^ and Molisch* to such a 

 withdrawal of water from the cell, that the cell dies on this account. Ac- 

 cording to this, death from frost would be a simple process of drying up. 

 The investigators support their theoi-y by the physical process, that, in 

 freezing swollen colloidal substances, pure water will be cr}'stallized out, 

 and the colloidal substance, thus gradually dr}dng, becomes stifif. 



In contrast to the above theory, is the one we hold, that death from frost 

 is no specific process of drying but should be sought in a molecular irre- 

 parable destruction of the protoplasmic structure. This destruction is 

 expressed mechanically as well as chemically. The destructive tempera- 

 ture is specific for each variety, each individual, each part of the plant and 

 each method of growth of any plant part, but is not directly connected with 



1 Compare Kunisch, H., Vsher die ttitliche Wirkung niederer Temperaturen auf 

 die Pflanzen. Inauguraldissertation. Breslau 1880. — Sachs, Landw. Versuchs- 

 stationen 1860, p. 196. 



2 Landwirtschaftl. Jahrbucher 1886, p. 490. 



3 L.OC. cit., . 534. 



4 Molische, tJber das Erfrieren der Pflanzen. Jena 1897. 



